Interferometer



Sept. 30, 1952 A. H. -MIRAU 2,512,074

INTERFEROMETER Filed March 27, 195o 2 SHEETS-SHEET `1 ArToRNEY Patented Sept. 30, 1952 i Viv...

PAt

i 'i INIEEFEROMETER Application Mar h 27, 1950;

Bhe present: inventi'on-y relates, .to interferon. eters andL other` rmea-surementv apparatuss (for: instance; for. studying; supercialapolisln orthe re1- fractive index xof` transparent,` liquidsior solids) based upon interferencev methodigineasure'menta of; differences; of., optical paths.. My. invention; consists. chiefly, nsseparati'ng. light; into V.twoheams-`1 byV meansloflaseparator including at semie-reect.- inglayer, in, combination withiat: leastiorieimirfroi on'othenoptcal` deviceicapable,y `ofi;giving-,sai'df`` beams. on,V .their wayl to the. viewingsystem=,. two;y substantially'. equal optical f paths; producing;ithe. phenomenon of interference..`.

' Other;tenturesofr my;` intention'.vvillappear in theifo1lowing'-1detailedi descrptioniofospeci'c emi. bodixnenltsethreof; Withreferenceto-` theI accom-- r panyingydrawings, given :by Way ofigexarnplen`f;1.:ndi.k inswhich': Y

Eig; l; isna perspective.vewvofeani interferometenrnadeaccording.l tozmyinvention,v A i Figs. 2 and 3 are views on a largerl scale show-H ing ,respectively in partial. axial? section -and'i side view, with-parts cut-away., certain.: parts cfr-this. apparatus-; l

Eig.. 4;,is a. diagramiillustratingzthe optical operat'ionzofithe systemw, s

Eig's. 5 ,.and. .diagrainrnaticallyshowninA eleva v tional -view:.,.andingplaniviem angular;V displacemments..V of theoptical;..axislof:=the apparatus; Y

Figtg'lzisza diagranirsanalogouss. 13o-that ofeiliigmig'.v relating.:toanotheriembodimentonthesinventin.

Accortdingpcto my. invention: Iainterposet acrossthe path of light rays travelling from a-suitable`v 1igl1t: .so.urcea to. a; viewingl, device rafters passing throughorlimpirigingpn Lthe medium to be stud.; iene-1 ai., separator device., essentially constituted1.. by,at;, least.; one semi-transparent',thinclayerrcae pable; in combination .withatfileast oneiA irfrcrf:4 or other optical device, of dividing the lightbeamh intostwoportons having.substantiallytequal :optif calmaths.,ancllgivingthusrisestoizinterterencesg;

.This;sell.alatonfis-i4 constituted irnparticularl:by` two tra.nsnarenti plates .l zffxFigstia and 4);. ofi: Suitable thicknessesI eithersequal :oi-mot; havingtY for. instanceftplane faces; pref eraloly.` Iparallel-t and pclishednatleast one of `.theseapla't-es carrying-thel above, rmentioned lthinplayerfa one,th'elasurfaceLIM thereof which; faces ..the` othenplatea. this zlayerrA beings-constituted;for.:instance".bytaxmetalhclzdeeaposit as well known in this art.

If it desiredsfor,instance-,toxamine ,through ayewingiopt.. al yjstemciiiagrannnaticallyJreprea sente. -0 Fie, piec P uminatediby a"sourcezslsupposemto bes locate onthe-fsanaeusidezasithe viewingifsystemNsse seriaplpNdfrszrsr HiFi-ance- Marclr1949 V 'ja-elegge@ (c1. zas-14) separator 31. is'u combined. JWith-y a-Y refer'eric'ersurface*y or mirror 4, disposed on the same sideiasfl'enslLw foiuinstanceiy onf-i` idrl'en's', and. arrangedi in such manner as. to sto uti alsmall portion of-'thef-in cident: beam. ThisAv mirronhowever, Will be ofsulicientarea. to avoid',` transmission of parasitic-V y rayst'oward;theviewingsystem.v

Eonpracticalpurpo'ses; *ifn it is desired to pro--A Vide va microinterferometen intended either to Idee;

termine the position of a polished surfaceorto study.- thesupercial polish l thereo'igvvthe dens L ofcFi'gs ltwill be fvreplaicedi by:in,microscopeolitec;v tiveii (Ei/g.: 2*) inicorxrbination-fwitlr a.: light source Sadisposed. at any. suitable point of-theappara'-V tus;i tori. instanceaarranged'1int-thesainfief` manner f* as;immetallographic devices of the usualltype,

that isa toisay dispo'sed1-ffor'instance late'rially'f'fto-i therameioitheapparatusf (Fig-1v 1l)5,l. with: semietransparent plate or a--total re'eflectitm`L prism. or y anniy other device 1 permitting '-l transmis-- sioni ofea'.-lightbeamltoward ytheeobjeett'oibe illu' minatedj; Without` interfering with visionJK through the eyelpiece8-"'of2= theflapparatfiis: Th'efus'eful" the fside .iof:th`e=-1object ATand-I thei'eldi of lthemicrow scope; Thisiield is, forfmostlrnicroscopesfrela tivelyismallasf-comparedwith the-dimensions of* theobjectivelensess Mirror dmayzbe constitut'ediforinstance; either .by a, metallic criepositifforlmedcnr theesurfacefof* metallic' pellet, i off plane; spherical;v cylindrical 'ort' other-shape which pellet-may heA either'v- -gled or not on the surface of said objectV-andf-may-" bet` either removablevor moti-Withl respect 'tovthe remainder of-`-the apparatus; When use f-isrmade of a;Y -metalli'c- 'ciepositf one'thel surface of the"Y obl jectivef this deposit f-maylv consist of"-vaporized aluminium it Jsuces'-to;I place one this surface# -durin'g\tnel-vaporizing of? aluminium, a' protectionelement Ywhich makessitfpossible `to `ldeposit metal:L onlyy inside' 'fa lsmall circle centered Ion'v the" objec tiveJaxis-ran'd Offafdiametersubstantiallyequalto" theeldlofithemicroscope@l Such =an amaaratiis,l includingtlie essentialele" ments whichfli'aveljjiist been'-described;"tbgetherf with` means efor locating Yithe separator and the# ohiectiveliwithirespect to` piece-ein `suitable land preferablyadjustahlJrelatiVef -csi-tions work'sf as have a perfectly plain and polished surfacef which equal optical paths can be obtained through a suitable adjustment of the relative positions of the elements, any small inequalities in the surface of P produce interference fringes which are observed through the eye-piece on the surface that is being examined and follow all the details thereof as visible for instance atA 9 on Fig. 6, unequalities resulting in corresponding unequalities I in said fringes.

It vis therefore possible, by means of such an apparatua-to examine and to measure the nish of surfaces.

=But such an apparatus also? makes it possible to, determine, with a high precision and without material contact, the relative position of a polishedrsurface, or even to dene the direction of this surface, by imparting the necessary movement to one of the elements the position and direction of which define the interference phenomenon.

Thus, according to a preferred feature of my invention, the apparatus makes it possible to modify at will the direction of the incident beam or of the optical axis of the apparatus with respect tothe surface or objectto be studied, or inversely. Figs 5 and 6 diagrammatically show, in this` respect, that variation of the angle M between optical axis A-A and surface P. involves a variation of the distance d between fringes.

(which are the intersection with surface P of the interference plane shown on a greatlyenlargedv scale on Fig. ).A Likewise, if 'axisA-A is rotated in space about a vertical vaxis Z-Z, the direction ofthe fringes varies. They assume for instance the new direction indicated in dotted lines at 9 (on these dotted lines and in order not 4to complicate thedrawing, notches I0 are not shown). Therefore by displacing the optical axis, the operator gets new possibilities of examination and measurement.

.I will now` describe the embodiment of Figs. l to 3,4 which makes it possible both to adjust the objective along its axis and to vary the direction thereof.

According to this embodiment (Figs. 1 to 3), the objective 5 is screwed in a piece II which supports, at the base thereof, separator l-2-3, this screwing assembly making` it possible to achieve a preliminary focussing of the objective on mirror 4, by reection on the semi-transparent layer 3 of the separator. Piece II in turn is screwed in the frame I of the apparatus, withmeans for controlling from the outside the relative rotation of these two parts, which means may consist of a sleeve I2 surrounding the lower part of,.cylindrical frame 6 and connected with piece II through a screw I3 extending through a slot I4 `of the frame.` By operating this sleeve I2, the objective can be focussed on the piece P to be studied, opposite which the whole of the apparatus is positioned through means which will'now be described.

In `vorder to determine the operating position or positions of the apparatus withrespect vto the piece or object to be examined, I make use, in

the embodiment illustrated by the drawing, of a swivel mounting including a base I5 adapted to be brought, for insta-nce through a plane face I6, into contact or close to piece P, with at least one hole I'I for the passage of the light beam, this base including a spherical portion I8 the center O of whichis for instance in plane 'I6 and inside hole I'I, and on which can rest the lower surface, also of spherical shape, of frame E. Advanta- `geously, in order to make it possible for frame 6 to support swivel base I5, I provide between them a spring connection I9 which does not prevent relative angular'displacements thereof.

Thus, the frame 6 of the apparatus can be givenany desired displacements, for instance of relatively small amplitude about any axis passing through center O, which displacements make it possible, the fringes being visible at the center of the field, of modifying at will their spacing and their direction, according to the type of surface that' is studied, without substantial displacement thereof in the eld. The smoothnessv of this adjustment makes it unnecessary to usethe slow movements usually applied in the art ing such that it allows for displacements of theapparatus' about center O and also makes it possible to displace base I5, in particular according'to the dimensions of the pieces or ob.- jects to be examined. y

Such a connection will preferably supply three degrees of freedom and will be obtained forinstance: either by means of a swivel arm, or,-'in a simple manner, as shown. by the drawing,.'by means of an elastic arm, constituted by a spring leaf 22 fixed in a removable manner and adjustable in height, at 23, 24, respectively on colum 30 and frame E. l

`The device illustrated by the drawing makes it possible both to move the swivel slightly on the piece and to vary the direction of the optical.

axis N -N ofV apparatus 6; it is therefore possible to adjust at will the direction and spacing' of the fringes in a very simple manner.' Furthermore, the setting in position is instantaneous whatever beV the thickness of the pieces to .be examined, which involves very quick control.y

The invention is still concerned with certain c features relating to the illumination by means of j First, it is of interest to place this source, as.' visible onFig. 1, at the upper part of the 'ap-- paratus, that is to say of tube 6, which reduces." the space occupied by the head of the apparatusi.

of the eye-piece carrier and interchangeable therewith. It is then possible to make use either of the arrangement shown or of one according to which the light source would be disposedjat the top of tube 6 and eye-piece 8 laterally, both devices cooperating in both cases with semitransparent mirror lor any other equivalent RISERS.

Finally, the apparatus is' supplied in a case or chest 2'I Which may have several functions, for instance: to house the apparatus, to supply electric current, for instance, either byA means of a transformer 28 for a stationary installation, or-v by means of a, pocket battery 29, for displacements, to house the fixation system including pedestal 2l and column 20.

I'he above considered application of the apparatus to the measurement of superficial states is in no Way limitative. Apparatus of this kind might be used for checking up the constancy of the refractive index of a transparent liquid or for measuring the difference between this index and that of a reference medium. It suflices for this purpose to interpose between the objective and the separator system the reference fluid and to pass the fluid to be studied between the separator system and surface P, Fig. 4. A variation of the index will be disclosed by a displacement of the interference fringes, easy to measure and which permits of calculating said variation.

Likewise, my invention may be applied to the observation of transparent matters and for instance of biological preparations. It sufces for this purpose to dispose the preparation to be examined on a, perfectly polished metallic surface; discontinuities in the interference fringes will then be due to differences in the refractive indexes of the substances through which the light passes and will then disclose details which are not obtained with the usual methods, if light absorption by the substances that are examined is uniform.

It should further be understood that the optical diagram of Fig. 4 is in no way limitative and that the relative positions of the incident and reflected beams, same as those of the optical devices and of the separator, might be different. Thus I might, in some cases, and in particular when it is desired to determine the refractive index of transparent bodies, combine with the same separator two optical systems or objectives such as LL' (Fig. 7) with two mirrors or reference surfaces DD'.

An incident ray arriving at AB through objective L can be divided into two rays having, as their optical paths ABCDEG and ABCDE'G', these two rays being then observed in objective L'.

One of the objectives, L, can therefore serve merely for illumination, and the other one, L', for observation. But observation might also take place concurrently on both sides, respectively through objectives L and L'.

My apparatus has many advantages, in particular greater simplicity, higher precision and greater facility of handling.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts Without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

1. An apparatus for studying by interference of light a surface to be tested which comprises, in combination, a light source, lens means for concentrating light rays from said source into a beam converging on said surface, a single partly reecting and partly transparent element disposed on the other side of said lens means from said source across the light beam issuing from said lens for dividing it into two elementary beams, a mirror located between said dividing element and said lens means having its reflecting face turned toward said element for equalizing the optical paths of the elementary beam reected on said element and of that passing through said element reflecting on said surface to be tested and passing back through said element, said mirror and said dividing element extending across the optical axis of said lens perpendicularly thereto, and a viewing device arranged to receive both of the elementary beams leaving said dividing element.

2. An apparatus according to claim 1 in which said mirror is carried by the external surface of the lens means.

3. An apparatus according to claim 1 in which 'said Viewing means are located on the same side of said dividing element as said source.

4. An apparatus according toI claim 1 including a frame, a sleeve supporting said dividing element mounted in an adjustable manner in said frame and means for mounting said lens means in an adjustable manner in said sleeve.

5. An apparatus according to claim 1 including a frame, said light source being carried by said frame laterally with respect to said lens means.

6. An apparatus according to claim 1 including a frame having a vertical tube with a side branch, and tubular elements for holding said light source and said lens means interchangeably engaging said tube and said side branch.

7. An apparatus according to claim 1 including a frame, a foot for said frame adapted to be placed on a piece to be examined, andswivel means for connecting said foot with said frame.

8. An apparatus according to claim 1 further including a base adapted to rest on the surface to be tested, a frame for holding said dividing element and said mirror, and means for interconnecting said frame with said base with three different degrees of freedom.

9. An apparatus according toI claim l further including a base adapted to rest on the surface to be tested, a frame for holding said dividing element and said mirror and a spring arm for interconnecting said frame with said base.

ANDRE MIRAU.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,724,527 Spierer Aug. 13, 1929 2,151,631 Williams Mar. 21, 1939 2,472,991 Sukumlyn June 14, 1949 yFOREIGN PATENTS Number Country Date 443,184 Great Britain Feb. 24, 1936 569,046 Great Britain May 2, 1945 602,459 Great Britain May 27, 1948 OTHER REFERENCES Interference Microscope For -Testing Surfaces; published in Industrial Diamond Review, vol. 6, lSeptember 1946, pages 276-279. Copy in U. S. Patent Office Library. 

